include/android-base/properties.h

/*
 * Copyright (C) 2016 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#pragma once

#include <sys/cdefs.h>

#include <chrono>
#include <limits>
#include <optional>
#include <string>

struct prop_info;

namespace android {
namespace base {

// Returns the current value of the system property `key`,
// or `default_value` if the property is empty or doesn't exist.
std::string GetProperty(const std::string& key, const std::string& default_value);

// Returns true if the system property `key` has the value "1", "y", "yes", "on", or "true",
// false for "0", "n", "no", "off", or "false", or `default_value` otherwise.
bool GetBoolProperty(const std::string& key, bool default_value);

// Returns the signed integer corresponding to the system property `key`.
// If the property is empty, doesn't exist, doesn't have an integer value, or is outside
// the optional bounds, returns `default_value`.
template <typename T> T GetIntProperty(const std::string& key,
                                       T default_value,
                                       T min = std::numeric_limits<T>::min(),
                                       T max = std::numeric_limits<T>::max());

// Returns the unsigned integer corresponding to the system property `key`.
// If the property is empty, doesn't exist, doesn't have an integer value, or is outside
// the optional bound, returns `default_value`.
template <typename T> T GetUintProperty(const std::string& key,
                                        T default_value,
                                        T max = std::numeric_limits<T>::max());

// Sets the system property `key` to `value`.
bool SetProperty(const std::string& key, const std::string& value);

// Waits for the system property `key` to have the value `expected_value`.
// Times out after `relative_timeout`.
// Returns true on success, false on timeout.
#if defined(__BIONIC__)
bool WaitForProperty(const std::string& key, const std::string& expected_value,
                     std::chrono::milliseconds relative_timeout = std::chrono::milliseconds::max());
#endif

// Waits for the system property `key` to be created.
// Times out after `relative_timeout`.
// Returns true on success, false on timeout.
#if defined(__BIONIC__)
bool WaitForPropertyCreation(const std::string& key, std::chrono::milliseconds relative_timeout =
                                                         std::chrono::milliseconds::max());
#endif

#if defined(__BIONIC__) && __cplusplus >= 201703L
// Cached system property lookup. For code that needs to read the same property multiple times,
// this class helps optimize those lookups.
class CachedProperty {
 public:
  explicit CachedProperty(const char* property_name);

  // Returns the current value of the underlying system property as cheaply as possible.
  // The returned pointer is valid until the next call to Get. Because most callers are going
  // to want to parse the string returned here and cached that as well, this function performs
  // no locking, and is completely thread unsafe. It is the caller's responsibility to provide a
  // lock for thread-safety.
  //
  // Note: *changed can be set to true even if the contents of the property remain the same.
  const char* Get(bool* changed = nullptr);

 private:
  std::string property_name_;
  const prop_info* prop_info_;
  std::optional<uint32_t> cached_area_serial_;
  std::optional<uint32_t> cached_property_serial_;
  char cached_value_[92];
  bool is_read_only_;
  const char* read_only_property_;
};
#endif

static inline int HwTimeoutMultiplier() {
  return android::base::GetIntProperty("ro.hw_timeout_multiplier", 1);
}

} // namespace base
} // namespace android

#if !defined(__BIONIC__)
/** Implementation detail. */
extern "C" int __system_property_set(const char*, const char*);
/** Implementation detail. */
extern "C" int __system_property_get(const char*, char*);
#endif